The Defence Force knew a bay near Devonport's naval base had been contaminated by the historical use of toxic fire-fighting foam for two years before it told the Auckland Council.
Tests results just released to RNZ under the Official Information Act show Defence knew the area was contaminated in early January 2016.
Councillors were only briefed on the contamination found in Ngataringa Bay yesterday.
Auckland Council said it's particularly interested to know the impact the toxic foam could have had on the marine life in the water, and people and animals who swim there.
Until last week the Defence Force had indicated contamination problems were limited to sites at Ohakea and Woodbourne.
On Thursday 22 the council's chief operating officer Dean Kimpton asked the Government about the status of investigations in Auckland, and asked for information. Six days later Defence confirmed Devonport Naval Base and site area, and Ngataringa Bay, were contaminated.
Defence is still investigating whether there's contamination near its Whenuapai Base but a former site at Hobsonville has been cleared.